1. Field of the Invention
This invention relates to a method for measuring a surface profile of a material contained in a container by use of a laser beam, more particularly, but not exclusively, to a method for optical measurement of a top surface profile of charges in a blast furnace.
2. Description of the Prior Art
In a blast furnace, coke and iron ore are alternately poured from the furnace top into the furnace. Therefore, the top surface of the charges in the furnace usually takes on a concave shape. The profile of the surface is very important in terms of the fuel consumed by the furnace. This is particularly significant in view of the need to conserve resources.
To control the top surface profile for the optimal fuel consumption, precise measurement is essential. In such measurement, remote control is necessary because of the extremely high temperature and pressure inside the furnace.
There is known an optical surface profile meter for measuring the top profile of charges in a blast furnace by the use of laser beams. The profile meter has a light emitter and a light receiver. The light emitter issues laser beams onto the top surface of the charge in the blast furnace, and the light receiver receives the laser beams reflected by the top surface of the charge. The surface profile of the charge is determined from the light emitting angles (projection angles) and light receiving angles (reception angles) by triangulation.
The prior art used a light receiver with a large field of view. Use of a light receiver with a large field of view eliminated the need for a movable receiver since the receiver could receive reflected light beams over a large range of reflection angles while fixed in one position. In other words, the receiver did not have to follow or track changes in the reflection angles of the reflected light beams. This is important in view of the technical difficulties in achieving exact and simple tracking.
A light receiver having a large field of view, however, has the drawback of a low resolving power. The low resolving power makes precise measurement of the surface profile of a charge in a blast furnace next to impossible. For example, if the resolving power per unit field of view of light receiver with a large field is 1/100 of the total field, the overall resolving power is only 1/100 of the total field.
On the contrary, if the resolving power per unit field of view of the receiver with a small field is 1/100 of the total field, supposing its unit field is 1/10 of the total field, overall resolving power would be 1/1000 of the total field.
Therefore, when a high resolving power is necessary, e.g., when it is desired to precisely measure the profile of the top surface of a charge in a blast furnace, a light receiver having a small field of view must be used. Such a receiver, however, has to be made to move in accordance with the change of the reflection angles of the light beams reflected from the top surface of the charge, which is, as explained above, technically difficult.